The probabilities of A, B, C solving a problem are 1 / 3,1 / 4 and 1 / 6, respectively. If all the three try to solve the problem simultaneously, find the probability that exactly one of them will solve it.
The probabilities of A, B, C solving a problem are 1 / 3,1 / 4 and 1 / 6, respectively. If all the three try to solve the problem simultaneously, find the probability that exactly one of them will solve it.

Given : let A, B and C be three students whose chances of solving a problem is given i.e, P(A)=\frac{1}{3}, P(B)=\frac{1}{4} and P(C)=\frac{1}{6}
\Rightarrow \mathrm{P}(\bar{A})=\frac{2}{3}, \mathrm{P}(\bar{B})=\frac{3}{4} \text { and } \mathrm{P}(\bar{C})=\frac{5}{6}
Now, \mathrm{P} (excatly one of them will solve it) =\mathrm{P}(\mathrm{A} and \operatorname{not} \mathrm{B} and \operatorname{not} \mathrm{c})+\mathrm{P}(\mathrm{B} and \operatorname{not} \mathrm{A} and not \mathrm{C})+\mathrm{P}(\mathrm{C} and not A and not B)
\begin{array}{l} =\mathrm{P}(\mathrm{A} \cap \bar{B} \cap \bar{C})+\mathrm{P}(\mathrm{B} \cap \bar{A} \cap \bar{C})+\mathrm{P}(\mathrm{C} \cap \bar{A} \cap \bar{B}) \\ =\mathrm{P}(\mathrm{A}) \times \mathrm{P}(\bar{B}) \times \mathrm{P}(\bar{C})+\mathrm{P}(\mathrm{B}) \times \mathrm{P}(\bar{A}) \times \mathrm{P}(\bar{C})+\mathrm{P}(\mathrm{C}) \times \mathrm{P}(\bar{B}) \times \mathrm{P}(\bar{A}) \\ =\left[\frac{1}{3} \times \frac{3}{4} \times \frac{5}{6}\right]+\left[\frac{1}{4} \times \frac{2}{3} \times \frac{5}{6}\right]+\left[\frac{1}{6} \times \frac{3}{4} \times \frac{2}{3}\right] \\ =\frac{15}{72}+\frac{10}{72}+\frac{6}{72} \end{array}
=\frac{31}{72}
Therefore, The probability that excatly one of them will solve the problem is \frac{31}{72}